We will look at how to mount PCBs in this article. Once the circuit board assembly is complete, the next step is to install it in its application area.
If you already have an outer plastic or metal case, you only need mounting holes drilled into the board. But you can also get a slide-in mounting enclosure to hold the board.
Either way, you’ll most likely require mounting holes, so we’ll start from there. Here’s how to mount a printed circuit board.
What Are Mounting Holes?
Mounting holes are slots drilled through printed circuit boards to provide a securing point when attaching the PCB to a chassis or enclosure.
These holes usually sit on the board’s corners and have annular rings to create stable surfaces for the fastening hardware to hold them in place.
Mounting Hole Types
Mounting holes can either have a metal plating or be plain holes, depending on whether they are conductive or non-conductive.
Plated Mounting Holes
The metal plate in these holes provides electrical connections between the layers inside.
But since the slot will host the fastener, the metal plate cannot connect to an electrically charged layer.
Instead, it links to a ground plane, creating an avenue for draining excess current from the circuit to the mounting frame. So these holes provide mechanical and electrical properties.
A PCB with plated and non-plated mounting holes
Non-Plated Mounting Holes
These holes purely provide mechanical properties. So you’ll most likely find them in keep-out zones to ensure they don’t interfere with other circuit sections.
What About Mounting Holes With Vias?
The plated mounting types of holes can have flat and plain annular rings or contain vias around the hole pad. These vias have three functions.
- Complement the plated hole by creating a ground connection between the layers. This connection is vital in high-frequency circuits because it minimizes EMI.
- Distribute mechanical stress from the fastener. Vias keep the holes tight and prevent damage over time caused by vibrations.
- Eliminate thermal stress by dissipating heat from the PCB and its electronic components via the internal copper planes. These holes provide a direct thermal path to the fastener, which directs it to the outer case.
Multiple PCBs positioned vertically with plated mounting holes at the same spot.
How To Design Mounting Holes
When designing mounting holes, the best option is to use plated holes because they provide the best corrosion and abrasion resistance. Plus, you can include vias to give the benefits listed above.
But either way, ensure the holes are broad enough to fit typical fasteners. This design provides flexibility to use different screws that match your electronic device case.
And consider ground nets when designing these mounting holes because they will not create noise.
On the contrary, this ground connection to the metal pin can drain unwanted charges out of the circuit, reducing EMI.
Also, ensure the design and circuit board have no floating metal bits because these can cause electromagnetic interference.
After drilling the holes, ensure the PCB board does not have surface scratches or dents. These defects can interfere with the soldering process.
A non-plated PCB mounting hole
How To Drill PCB Mounting Holes
First, determine the shape and size of the mounting hole you want to drill, then pick the most appropriate drill bit. Follow these steps after that.
- Use a drill press to punch the pilot holes while ensuring perfect alignment.
- Drill the holes and run an abrasive wheel around the hole edges to eliminate burrs.
- Select a plating material with high corrosion resistance to form the annular rings on both sides of the hole.
- Mirror the hole in the plating material and cut it to create the annular ring.
- Cut a copy of this ring (the two should align when layered above the other).
- Secure the rings using glue or clear tape to prep them for wave soldering.
How To Mount PCBs in Mounting Enclosures
You can mount printed circuit boards in enclosures using either of the following methods.
Standard Mounting Bosses
Standard mounting bosses are protrusions molded from the inner surface of PCB enclosures.
These pre-formed structures provide the fastest and easiest way to mount circuit boards and feature screw threads for inserting fasteners.
So when drilling mounting holes in your PCB, align them with these bosses.
And during installation, align the holes with these protrusions, then insert the screws and fasten them.
Custom Mounting Standoffs
If your PCB already has mounting holes, you can order an enclosure with custom-positioned mounting bosses.
This option is costlier than using cases with standard mounting bosses, but you might not have to go through the hassle of drilling the board and plating the holes.
A batch of ready-to-use PCBs
A cheaper alternative is to use mounting standoffs with adhesive bases.
These pieces go through the PCB mounting hole and stick to the enclosure surface.
And they feature flanged designs that lock boards in position without requiring screws.
Slide-In Mounting Guides/Rails
Guide rails molded into the enclosure’s walls allow the PCB to slide into position for fastener-free securing. And you can unmount the boards quickly, as well.
This option is ideal for installing multiple printed circuit boards in one enclosure because it simplifies management and maintenance.
Factors To Consider Before PCB Mounting
Consider these four factors before buying PCB mounting enclosures for your project.
Board Size and Shape
The mounting enclosure should be large enough to accommodate the PCB and have the right shape for perfect fitting.
Mounting Hole Position
The mounting holes present in the board should match the mounting bosses’ location.
Although you can punch the holes, drilling them during production is simpler. You’ll only have to screw them in place.
An unassembled radio frequency PCB with corner mounting holes
Electronic Component Height
Most modern PCBs have surface-mount devices, which are tiny and short.
But if your board contains through-hole components, consider their height because it forms the PCB’s width.
And they should fit in the enclosure, so ensure the case is wide enough to host the assembled board.
Some PCB components emit high heat levels when running, and circuit boards can get damaged when operating under extreme temperatures.
So consider mounting them with heat sinks or fans to transfer heat to the atmosphere.
Hardware To Consider for PCB Mounting
These pieces of hardware can help you during mounting. And some enhance your PCB’s performance.
- Screw grommets for fastening
- Mounting pillars for elevating circuit boards above the surface
- Spacers for spacing the PCBs above the surface
- Mounting blocks for making electrical connections between the board and chassis
- LED mounting hardware (LED spacers) for managing onboard LEDs
- Transistor insulators for heat transfer to heat sinks
- PCB fan to prevent overheating
- Card pullers to insert and remove PCBs in slide-in mounting enclosures
- PCB support to provide a flat resting area and minimize vibrations
An insulated transistor
So consider these hardware devices for the following applications.
- Data cabinets: Card guides, PCB spacers, and PCB supports
- Electrical cabinets: Screw grommets, PCB supports, and PCB fans
- Automotive: PCB fans, LED mounting hardware, and spacers
- Office machinery/Consumer electronics: Transistor insulators, LED mounting hardware, and PCB supports
The process of mounting PCBs usually begins with drilling mounting holes. And these slots must align perfectly with the mounting bosses in the enclosure.
However, if you want to install multiple circuit boards in one case, you can get one with slide-in guides.
And remember to consider the hardware listed above to make your installation better.
That’s it for this article. Comment below to let us know your thoughts about this guide or if we left something out.